Block 3 Flashcards
what are the three phases of swallowing?
- oral phase
- pharyngeal phase
- oesophageal phase
what happens at the oral phase? (2)
- voluntary phase
- tongue pushing bolus to the back of the throat
what happens at the pharyngeal phase? (5)
- tongue blocks oral cavity
- soft palate blocks nasal cavity
- vocal folds close to protect airways
- oesophageal sphincter opens
- stimulated by tactile receptors in the oropharynx
what happens at the oesophageal phase? (3)
- bolus propelled down oesophagus by peristalsis
- larynx moves back to original position
- peristaltic waves moves gastric contents down into pyloric antrum
what nerve innervates the muscles of mastication?
trigeminal nerve
what is the chewing reflex controlled by?
nuclei in the brainstem
stages of the chewing reflex (5)
- presence of bolus initiates reflex inhibition of muscles, allows jaw to drop
- drop initiates stretch reflex of jaw muscles
- leads to rebound contraction, automatically raising jaw to cause closure of teeth
- compression of bolus against the lining of the mouth inhibits the jaw muscles again
- process is repeated
What is retropulsion?
food particles that are too large to pass through the pyloric sphincter into the small intestine are forced back into the body of the stomach
three phases of gastric acid secretion
- cephalic phase - secretion by anticipation of eating (smell/taste)
- gastric phase - secretion stimulated by distension of the stomach and by amino acids present in the food
- intestinal phase - stimulated by small intestine digestion and by amino acids
What are the stages of the secretion of gastric acid (5)
- Cl- and Na+ are secreted actively from parietal cells into the lumen of the canaliculus
- this creates a negative potential across the membrane that causes K+ and some Na+ to diffuse out
- carbonic anhydrase catalyses the reaction between CO2 and H2O to form carbonic acid. This dissociates into H+ and HCO3-
- H+ leave the cell through H+K+ ATPase anti porter, at the same time Na+ is actively reabsorbed
- H+ and Cl- mix together, they are secreted into the lumen the oxyntic gland
What is gastric emptying?
when the food particles are small enough they can pass through the pyloric sphincter
What does the cephalic phase of gastric activate? (3)
- cerebral cortex
- hypothalamus
- brain stem
what two components make up chyme?
- food particles
- gastric acid
Which nerves activate the stimulation of the salivary glands? (2)
- facial nerve
- glossopharyngeal nerve
What is released through the stimulation of gastric glands?
gastric jucie
which nerve activates the stimulation of the gastric glands?
vagus nerve
which cells release gastrin?
G cells
What is gastrin released in response to? (5)
- distention
- high pH
- caffeine
- Ach
- partially digested proteins
What does gastrin do? (4)
- increase motility of stomach
- relaxed pyloric sphincter
- strengthens contraction of lower oesophageal sphincter to prevent reflux
- stimulates gastric glands to secrete large amounts of gastric juice
What pH is gastrin secretion inhibited at?
pH <2
What is absorbed in the duodenum?
iron
What is absorbed in the jejunum? (4)
- folate
- glucose
- fatty acids
- amino acids
What is absorbed in the ileum? (2)
- B12
- bile salts
What is produced when dietary fibre is fermented in the colon?
short-chain fatty acids
Where does carbohydrate digestion begin?
mouth that salivates amylase
what does the acidic pH of the stomach do?
destroy salivary amylase
What happens to un-broken down starch?
cleaved by pancreatic amylase in pancreatic juice
what do brush-border enzymes do? (2)
- act on resulting a-dextrins
- clipping off one glucose at a time
what is maltose broken down into? (2)
- glucose + glucose
- broken down by maltase
what is sucrose broken down into? (2)
- glucose + fructose
- broken down by sucrase
what is lactose broken down into? (2)
- glucose + galactose
- lactase
How is carbohydrate absorbed? (4)
- monosaccharides pass from the lumen of the small intestine through the apical membrane
- via facilitated diffusion (fructose) or active transport coupled with Na+ (glucose + galactose)
- move out through basolateral surfaces via facilitated diffusion
- enter capillaries
How is protein absorbed? (3)
- begins in the stomach with pepsin
- enzymes in pancreatic juice (trypsin, chymotrypsin, carboxypeptidase, elastase) continue to break down proteins into peptides
- protein digestion is completed by two peptidases in the brush border
What does amino peptidase cleave off to?
amino acids
What does dipeptidase split?
dipeptides to single amino acids
where are amino acids absorbed? (2)
- duodenum
- jejunum
where do the amino acids enter and how? (2)
- capillaries
- via diffusion
How are lipids digested? (6)
- emulsification of lipid by adding bile salts
- digestion by lipase
- free fatty acids + bile salts forming micelles
- micelles cross the epithelium
- triglyceride + protein forming chylomicron
- chylomicron enters secretory vesicle
what do micelles transport?
soluble monoglycerides
where do micelles transport monoglycerides and why? (2)
- surface of enterocyte
- to be absorbed
What happens to fats inside the enterocyte (epithelial cell) (5)
- monoglycerides are resynthesised into TAG
- TAG is packaged with cholesterol + fat soluble vitamins in chylomicrons
- chylomicrons are released by excytosis in secretory vesicles at the basolateral surface of the enterocyte
- they enter lacteals (lymphatic vessels)
- chylomicrons cant enter capillaries as they are too large
What does the myenteric plexus stimulate? (3)
- muscles to contract in peristaltic waves
- promotes secretion of intestinal juices
- allows sphincter to open
what are cells of the liver called?
hepatocytes
what does the liver secrete?
bile
what does bile consist of? (6)
- water
- bile salts (form micelles)
- cholesterol
- lecithin
- bile pigments (main one is bilirubin)
- several ions
what do lipids combine with to form chylomicrons?
proteins
what do lipids and proteins combine to form?
chylomicrons
where do chylomicrons travel?
in the blood
what is removed in the blood by hepatocytes?
remnants of chylomicron
what does vLDL stand for?
very low density proteins
where do vLDLs form?
in hepatocytes
what is the role of vLDLs?
transport triglycerides synthesised in hepatocytes to adipocytes for storage
How are vLDLs converted to LDLs? (2)
- Apo C-2 activates endothelial lipoprotein lipase which removes fatty acids
- vLDLs are converted to LDLs
What % of cholesterol do LDLs carry?
75%
where do LDL deliver cholesterol? (2)
to cells throughout the body for…
- preparing cell membranes
- synthesising steroid hormones and bile salts
what happens if LDLs are present in excessive numbers? (3)
- deposit cholesterol in and around smooth muscle fibres in arteries
- forming fatty plaques
- increasing risk of CVD
what is the role of HDLs? (3)
- to remove cholesterol from body cells and blood
- transport it to the liver for elimination
- prevent accumulation of cholesterol in the blood
what does the body need cholesterol for?(6)
- myelin sheath
- plasma membrane
- intracellular transport
- cell signalling
- bile
- precursor for vitamin D and steroid hormones
sources of cholesterol
- food
- synthesised by hepatocytes (most)
What happens in cholesterol metabolism? (4)
- oxidised by the liver into a variety of bile acids
- 95% of bile acids reabsorbed from intestines, remainder lost in faeces
- in the colon, cholesterol can be metabolised by the colonic bacteria
- converted to coprostanol and excreted in the faeces
Name 5 things that control parietal cell acid (HCl) output
- histamine - stimulating
- gastrin - stimulating
- Ach - stimulating
- prostaglandins (E2 and I2) inhibiting
- somatostatin - inhibiting
How is the gut secretion stimulated? (4)
- gastrin released from G cells
- gastrin acts on CCK2 receptors on ECL cells to release histamine
- histamine acts on parietal cells H2 receptors to elevate CAMP that activates the secretion of acid by the proton pump
- direct vagal stimulation also provokes acid secretion and releases Ach that acts on parietal cells M3 receptors
How is gut secretion inhibited?
somatostatin excrete a tonic/inhibitory influence on G cells, ECL cells and parietal cells
What is the mechanism of proton pump inhibitors? (3)
- irreversibly blocks the H+K+ATPase of parietal cells
- reduces gastric acid secretion by up to 99%
- aids the healing of duodenal ulcers, reduces pain from indigestion
What is the mechanism of histamine H2 receptor antagonists? (2)
- competitively inhibit histamine actions at H2 receptors in upper GI tract
- inhibits gastric acid secretion
what is the role of antacids?
- directly neutralise acid
- mainly salts of magnesium and aluminium are used
What type of epithelium is the stomach?
simple columnar epithelium
what type of epithelium is the mouth, pharynx and oesophagus?
stratified squamous epithelium
what three structures are made up of stratified squamous epithelium?
- mouth
- pharynx
- oesophagus
What are the arteries that branch of the coeliac trunk? (5)
- left gastric
- right gastric
- left gastroepiploic
- right gastroepiploic
- short gastric artery
which nerve supplies the stomach?
vagus
what does the vagus nerve control? (2)
- secretomotor
- peristaltic movements
what does the sympathetic nerves control? (2)
- visceral
- vasculature
how long is the duodenum?
25cm
what are the 4 parts of the duodenum?
- superior
- descending
- horizontal
- ascending
describe the superior duodenum (2)
- peritoneal
- contains CBD
describe the descending duodenum (2)
- retroperiotneal
- receives CBD via hepatopancreatic ampulla (of Vater) at the major duodenal papilla
describe the ascending duodenum (2)
- duodenojejunal flexure
- ligament of treats
describe the horizontal duodenum (2)
- retroperitoneal
- IVC and aorta are posterior
What is pharmacodynamics?
how a drug works on the body
What is pharmacokinetics?
decided route of administration of a drug
What does ADME stand for?
- A - absorption
- D - distribution
- M - metabolism
- E - excretion
How are drugs absorbed? (4)
- diffusion
- carrier mediated (protein assisted)
- paracellular (between cells)
- efflux transport
the stronger the acid/base nature of the drug, the…
…harder it is to absorb them
what are peptic ulcers caused by? (2)
- bacterial infection
- disruption of the stomach mucosal lining
how you differentiate between a stomach and a duodenal ulcer?
- stomach ulcer - pain soon after eating a meal
- duodenal ulcer - pain 2-3 hours after eating
what do parietal cells produce?
protons to elevate pH of the stomach
what do neck cells produce?
lining for the stomach
what do chief cells produce?
pepsinogen
H+ is pumped into the lumen in exchange for what?
K+ via proton pump
what pharmacology can be used for acid secretion? (4)
- proton pump inhibitors
- produgs
- histamine inhibitors
- NSAIDS